1. Field
The invention relates to intermittent film transports, and particularly to a rolling loop transport with improvements for reducing the jitter to allow use of the transport in sophisticated video recording systems.
2. Prior Art
The basic concepts of the rolling loop transport may be found, for example, in U.S. Pat. No. 3,494,524, which describes generally a rotating rotor within a stationary stator system, wherein the rotor has a plurality of gaps for forming loops in respective portions of the film being introduced via an inlet sprocket, and removed via an outlet sprocket, both of which are disposed in the stator. U.S. Pat. No. 3,600,073 describes a more sophisticated rolling loop transport utilizing the concepts of the prior patent but including additional features which overcome some of the problems inherent in the more basic transport. The U.S. Pat. No. 3,600,073 utilizes a large plurality of gaps in the rotor, with an associated relatively short distance from the film inlet to the exposure gate wherein the film is exposed, and a prescribed larger distance from the gate to the film outlet. An inlet sprocket and an outlet sprocket are utilized to provide continuous film motion at the inlet and outlet of the transport. Thus, an increasing loop size is generated during the short movement of a rotor gap from the inlet to the exposure gate, while a decaying loop is generated within the rotor gap as it moves the longer distance from the gate to the film outlet. In such rolling loop transports, an unbalance of compressive forces in the film is induced due to the continual change of both the entering (building) and exiting (decaying) loop geometry. As a result, there is generated a rather complex series of longitudinal and transverse forces relative to the film length. Thus the film is elastically deformed in both longitudinal directions about the registration pins located in the region of the exposure gate, wherein the longitudinal deformation direction is dependent upon the circumferential positions of the loops relative to the exposure gate and the registration pins, as the loops travel within the confining stator. Obviously, any elastic deformation and deflection of the film at the registration pins during the exposure of the film (i.e., when performing the recording or reproducing process) causes a corresponding deterioration of the recording, particularly in recording processes utilizing very high density laser or electron beam recording schemes. Thus U.S. Pat. No. 3,600,073 partially overcomes the worst of the bidirectional forces of previous mention by employing a relatively complex arrangement of vacuum and pressure lines, manifolds, stator guides, film guides on the rotor, etc. In addition, the system employs a complex decelerating cam/pin means to slow the film prior to its engagement with the fixed registration pins located in the region of the exposure gate.
The registration pins conventionally utilized in the above-described rolling loop transport systems, serve to position and anchor the film in the exposure gate at the time of exposure thereof. But due to the small bearing area of the film on the pins, large film shafts due to elastic deformation of the film at the perforations thereof in contact with the pins, causes the film to shift in the gate during exposure which contributes to a smeared image and resulting recording deterioration.
U.S. Pat. No. 3,135,159 discloses a modified rolling loop transport which deletes the second or outlet sprocket, wherein the film loop is not decayed during the distance that the rotor moves the loop from the exposure gate to the film outlet. In addition, the latter patent provides a vacuum platen over the entire distance extending from the inlet to the outlet of the film, and thus provides a vacuum platen between the gate and the outlet as means of controlling the movement of the loop while further stabilizing the film. The latter system provides for generation of the rolling loop immediately at the entrance of the system, i.e., provides for the generation of the entire loop size immediately upon introducing the film from the inlet sprocket into the film inlet between the stator and rotor. The inlet area vacuum platen is employed to hold the film motionless while the loop is being formed at the inlet by continuing to feed the film into the system via the inlet sprocket. The subsequent engagement with the single gap of the rotor forces the loop along the vacuum surface to the exposure gate.
The configurations of the above-described rolling loop transports fail to provide adequate pull-down rates and/or sufficient stabilization of the film during the exposure period to allow their use with highly sophisticated video recording schemes utilizing electron and/or laser beam recording techniques.